Eligibility doubts about two Nationals MPs

Two more Turnbull government MPs could be tripped up by the High Court after it ruled a Liberal candidate was ineligible to take the Senate seat of former cabinet minister Fiona Nash.

Ms Nash was disqualified by the High Court on October 27 because she held dual citizenship, in breach of section 44 of the constitution.

Hollie Hughes was the next candidate on the NSW coalition Senate ticket at the 2016 election behind the then-Nationals deputy, and was due to take Ms Nash's seat following a court-ordered special count.

However, the court on Wednesday ruled Ms Hughes could not take up the seat because she was also disqualified.

Ms Hughes was appointed a part-time member of the Administrative Appeals Tribunal on July 1 this year, which the government admitted to the court was an "office of profit under the Crown".

The ruling has heightened concerns inside the government that assistant minister David Russell - who is facing his own High Court battle - and Nationals colleague Barry O'Sullivan might be disqualified for similar reasons.

Attorney-General George Brandis wouldn't be drawn into speculation about the pair's future until the court's reasoning in the Hughes case is made public.